What Weather Is the Fault of Climate Change?

By Heidi Cullen

March 11, 2016

Image

CreditPatrick Kyle

LIKE politics, weather can be a contentious subject, especially when you throw climate change into the mix.

One view holds that no single storm or drought can be linked to climate change. The other argues that all such things are, in some sense, “caused” by climate change, because we have fundamentally altered the global climate and all the weather in it.

While true, this “all in” philosophy doesn’t adequately emphasize the fact that not all of the extreme weather we experience today has changed significantly. Some of it is just, well, the weather.

But some of our weather has changed significantly, and now a new report from the National Academies of Sciences, Engineering and Medicine has outlined a rigorous, defensible, science-based system of extreme weather attribution to determine which events are tied to climate change.

Like the surgeon general’s 1964 report connecting smoking to lung cancer, the report from the National Academies connects global warming to the increased risk and severity of certain classes of extreme weather, including some heat waves, floods and drought.

This is an important development. Climate change can no longer be viewed as a distant threat that may disrupt the lives of our grandchildren, but one that may be singled out as a factor, possibly a critical factor, in the storm that flooded your house last week. The science of extreme weather attribution brings climate change to our doorsteps.

Understanding how climate change is affecting extreme weather is critical for insurers, policy makers, engineers and emergency managers as they assess risk and figure out how to make communities more resilient. This knowledge can help to steer decisions on where and how to build or rebuild after a storm or flood, or whether to build or rebuild at all.

And those are decisions we’re going to face with increasing frequency as the planet continues to warm.

Scientists are now able to assess, in some cases within days, whether and how much the risk of such an extreme weather event has changed compared to the past — that is, before heat-trapping greenhouse gases altered our climate. This knowledge will help communities make decisions appropriate for today’s risks. These can include storm surge risk maps that reflect sea-level rise, better water management to reduce the effects of longer and more intense droughts, and improved floodplain management in increasingly flood-prone areas.

Climate change brings with it many existential threats — rising seas, acidifying oceans, species extinction. But the most immediate and costly threats result from the changing risks of extreme weather. Our perception of these risks has been almost entirely based on the past. That’s how insurance companies have assessed our premiums. But if weather risks change, and events that used to have a 1-in-500 chance of happening in any given year now have a 1-in-50 chance, insurance premiums will rise or insurance itself might become unavailable.

Here’s an example that underscores the predictive power of extreme event attribution: A recently published study in the journal Nature Climate Change analyzed record-breaking rains in Britain that flooded thousands of homes and businesses and caused more than $700 million in damage in the winter of 2013-14. Scientists found that such an event had become about 40 percent more likely. As a result, roughly 1,000 more properties are now at risk of flooding, with potential damage of about $40 million.

Climate change is, of course, never the only player in a so-called natural disaster. Many other natural and human factors are at play. Countless communities are vulnerable because of limited resources and poor infrastructure. Certain classes of extreme events will be relatively straightforward to dissect and attribute (heat waves, heavy rains, certain types of drought) while others are at the far edge of what science can now understand (tornadoes, wildfires and the frequency and intensity of hurricanes).

Heat waves, for example, are expected to become more common, intense and longer because of the increase in heat-trapping gases in the atmosphere. One recent study found that an extreme heat wave last May in Australia was made 23 times more likely because of climate change. When the numbers get that big, it’s fair to say that some episodes of extreme heat would have been virtually impossible (but never absolutely impossible) without climate change.

Drought is more complicated because of the multiple factors — temperature, precipitation, soil moisture, snowpack levels — involved. The California drought is an example of this complexity. While we now know that higher temperatures resulting from global warming are worsening the drought, current evidence indicates that the lack of precipitation in the state is not primarily a result of climate change.

Without the rigorous methodologies outlined in the National Academies report, we run the risk of attributing extreme weather to climate change based on sheer conjecture or political bias.

And sometimes it is easier to blame climate change than acknowledge inaction in the face of factors unrelated to the weather. For example, in a severe drought plaguing southeastern Brazil — including São Paulo, with a surrounding metropolitan population of about 20 million — some were quick to blame global warming. But in analyzing the underlying causes of this drought, my colleagues and I found, in a study published last year, that climate change was not a major influence. Instead, population growth, increasing water consumption and leaky pipes were the real culprits.

Science is giving us an increasingly clear picture of how global warming is changing the weather. Still greater investment in research is needed to ensure that we’re making the best possible decisions to protect our communities. We may not always like what we learn, but we can be certain that unless we take immediate action to slow climate change, its influence on our lives will only intensify.